RELATION OF WATEE TO THE PROTOPLASM 69 



intimately connected with the presence of water in its 

 substance. The importance of the ready access of the 

 latter is seen further from other considerations. We have 

 incidentally alluded more than once to the fact that the 

 liquid concerned in these osmotic currents is not pure 

 water only, but should rather be regarded as an extremely 

 dilute solution of various salts, &c. Though the protoplasm 

 opposes the passage of anything like a strong solution of 

 inorganic salts, it allows very dilute ones to enter the cell, 

 much as it does pure water. In this way the slowly diffusing 

 stream brings to the protoplasm of each cell the inorganic 

 materials which are absorbed from the earth, and enables 

 the matters elaborated or formed from them by the proto- 

 plasm to pass from cell to cell. The feeding or nutrition of 

 the various cells, together with the construction of the sub- 

 stances which minister to that nutrition, is thus dependent on 

 the transit of fluid about the plant in the way described. The 

 access of various gases is similarly made possible, for these 

 are dissolved in the liquid stream. The oxygen upon the 

 presence of which life depends is thus transported to each 

 cell, and the carbon dioxide of respiration is removed from 

 the seats of its liberation. 



The condition of turgescence is necessary also for growth, 

 and for various movements of different parts, enabling 

 them to adapt themselves to varying conditions of their 

 environment. Some plants, particularly those which are 

 aquatic in habit, and such parts of terrestrial plants as 

 contain but little woody tissue, are dependent on the tur- 

 gescence of their cells for the rigidity which enables them 

 to maintain their position in the medium in which they 

 live. The maintenance of the turgid condition of the cells 

 is further of the highest importance in enabling the inter- 

 change of water between contiguous cells to take place as 

 freely as possible, and without intermission. Flaccid cells 

 do not effect such interchange with sufficient readiness. 

 Flaccidity of an organ is attended by a partial collapse of the 

 tissue, which involves a diminution of the volume of its 



